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Question

A child is moving on a skateboard with a speed of 2 ms1. After a force acts on him, his speed becomes 3 ms1. Calculate the work done by the force, if the mass of the child is 20 kg.


A

1 J

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B

10 J

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C
20 J
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D
320 J
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Solution

The correct option is B

10 J


Given: initial velocity of the child, u=2 ms1, final velocity, v=3 ms1, and mass, m=20 kg.

Initial kinetic energy =mu22
Final kinetic energy =mv22

Change in kinetic energy =mv22mu22
m×(v2u2)2=20×(94)2=50 J

Work done by force = change in kinetic energy of the child

Therefore work done by the force is 50 J


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